Dielectric elastomer (DE) is a promising electroactive polymer. As DE material, rubbers are often filled with functional particles to improve their electromechanical performance. However, the filled particles also bring stress softening, which is known as Mullins effect. In this paper, we prepared the carbon nanotube filled silicone elastomer (SE) as DE composite and modeled its Mullins effect using the pseudo-elastic theory. Then, the thermodynamics of DE was combined to predict the idealized electromechanical softening behavior. Two cases are considered: linear dielectric and saturated dielectric. For linear dielectric with an initial force, “residual strain” will appear after every voltage-controlled cycle, and instability may be eliminated in reloading. For saturated dielectric, the material response changes a lot after saturation, which also affects the subsequent softening behavior. At last, viscoelasticity was further incorporated to account for rate-dependent softening deformation, and we also carried out some simple electromechanical experiments on VHB 4910 to explore its softening behavior. This work may lead to a better understanding of the softening behavior in DEs undergoing electromechanical coupling situations.

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